1. Field of the Invention
The present invention relates to techniques and devices for use in commercial fishing.
2. Description of the Prior Art
In recent years, there has an increasing public concern over the number of porpoises which are trapped in seine fishing nets and inadvertently killed in the practice of conventional purse net techniques of commercial fishing. Because porpoises tend to school in the vicinity of yellow fin tuna, a major species in commercial fishing, they are frequently trapped in fishing nets which are set by tuna fishing boats. One technique for locating tuna is to first locate a school of porpoises, since there is a fair likelihood that tuna will be found in the immediate vicinity, frequently in schools beneath the porpoises at greater depths. While commercial fishermen release any porpoises trapped with the fish, many porpoises are killed because their snouts and flukes become entangled in the webbing of the seine nets beneath the surface of the water, and the animals are unable to surface in order to breathe.
Various types of porpoise gates have been deviced for use with seine nets in order to allow porpoises to escape. Such conventional techniques usually allow a portion of the perimeter of an encircling net to the collapsed so that the porpoises are able to swim over the top of the net at the collapsed section. However conventional techniques of this type have been unsatisfactory because the release of porpoises is only accomplished after lengthly delays in collapsing and again erecting the portion of the net across which the porpoises find a pathway to freedom. The delays involved prolong the period of captivity for the porpoises, which sometimes become entangled in the net webbing and drown. Also, the lengthy delays in rasising the net perimeters once they have been lowered frequently allows the tuna, or other entrapped fish to escape along with the porpoises. Furthermore, because collapsing the net is such an arduous process, the porpoises frequently move to an area of the net remote from the collapsed section before lowering of that section has been completed. They then do not find their way to freedom, but remain within the net.
Another technique which has been attempted in order to prevent porpoises from becoming entrapped within seine nets is to broadcast underwater recorded sounds of killer whales or sharks in the area of the porpoises before the seine net has been completely set in order frighten the porpoises away. This has likewise proven inadequate, however, since fish are just as likely to respond to such sounds as are porpoises, and are just as likely to leave the area. Moreover, the delay in closing the perimeter of the net allows the fish to escape, whether or not they respond to the recorded sounds.